There have been a copier and a scanner as a device to optically scan a document. A system for scanning a document used in these devices includes a platen system using a document scanning unit and a system using a sheet-through type auto document feeder (ADF).
FIG. 40 schematically shows a scanning mechanism by an ordinary document scanning unit. In the platen system, a document 11 to be scanned is placed on a contact glass 12. A carriage 15 with an irradiation lamp 13 and a mirror group 14 is moved along the document 11 to scan in the surface of the document. The carriage 15 is driven by a stepping motor not shown.
In this platen system, a movement rate of the carriage 15 with respect to the document 11 is controlled at the time of scanning the document. Thereby, the number of lines to be optically scanned per unit distance in the movement direction of the carriage 15 (this is referred to as auxiliary scanning direction) is controlled.
In other words, when a document enlarged with respect to the original document 11 is to be output, the carriage 15 is controlled so as to move slower than a case where a size ratio between the original document 11 and the output document is 1:1. When the carriage 15 move slower, the number of lines to be scanned per unit distance in the auxiliary scanning direction increases.
When the document 11 is reduced in size, the carriage 15 is controlled so as to move faster. When the carriage 15 moves faster, the number of lines to be scanned in the auxiliary scanning direction decreases. The scaling processing allows the document to be enlarged or reduced in the auxiliary scanning direction in such a manner as explained above. On the other hand, in the direction crossing the auxiliary scanning direction (this is referred to as main scanning direction), by performing electrical scaling processing on one-line data, enlargement or reduction is carried out.
In general, an electrical document size sensor is provided in a copier. This sensor detects the document size before the carriage 15 starts to move, that is, before the document 11 is scanned. Therefore, when a paper size scaling function is selected, the rate of scaling from the document size to a paper size is calculated before starting to scan-in the document.
For example, even if a document of any of various sizes such as A3, B4, A4, or B5 is placed on the contact glass 12 in portrait or landscape orientation, a process controller calculates parameters to control scaling before the carriage 15 starts to move. That is, the movement rate of the carriage 15 is controlled based on the parameters.
FIG. 41 schematically shows a scanning mechanism by an ordinary sheet-through type auto document feeder. In this case, a document 11 to be scanned is conveyed by a sheet-through type auto document feeder 16 with a document feeding mechanism so that the document 11 automatically passes through a scanning position.
During the processing, the carriage 15 remains fixed to the scanning position. That is, in the case of using the platen system, the carriage 15 is moved along the document 11 at a standstill, while in the case of using the sheet-through type auto document feeder 16, the document 11 moves toward the carriage 15 at a standstill.
The movement rate of the document 11 is controlled by the stepping motor not shown. When the document 11 is to be enlarged or reduced in the document feeding direction (which is the auxiliary scanning direction), the movement rate of the document 11 is controlled. That is, in the same manner as the platen system, enlargement or reduction is performed by changing a relative rate for movement between the document 11 and the cartridge 15.
When the sheet-through type auto document feeder 16 is used, a document size is detected by a mechanical sensor. In this case, the document size in the auxiliary scanning direction is detected at the point of time when scanning of the document 11 is finished. That is, at the time before the document is started to be scanned, the size of the document 11 in the auxiliary scanning direction is unknown. Therefore, it is impossible to calculate parameters to control scaling before the document 11 is started to be scanned. Accordingly, a feeding rate of the document 11 according to an enlargement ratio or a reduction ratio can not be controlled.
The same holds true for the direction crossing the auxiliary scanning direction (which is the main scanning direction). A document size in the main scanning direction is detected at the point of time the document 11 reaches a sensor position. Therefore, when there are documents 11 of various sizes, it is impossible to calculate parameters for controlling scaling before starting to scan the document.
The image of the document 11 scanned by the sheet-through type auto document feeder 16 is related, as a mirror image, to the image obtained in the platen mode in the main scanning direction. Therefore, at the time of outputting the image, the processing for mirroring, that the image is reversed left to right, is performed on the image.
Nowadays the copiers include a digital copier as against the conventional analog copier. The digital copier optically scans paper document or the like, and converts the scanned image signal to a digital image signal to perform image processing. Further, the digital copier includes a digital multifunction machine that has functions of a scanner, a printer, and a facsimile other than the copying function.
Some of the digital copiers and the digital multifunction machines (hereafter referred to as digital multifunction machine etc.) enlarges or reduces an image by performing electrical scaling processing on a digital image signal instead of its enlargement or reduction by mechanical control as explained above.
An example of such a device is disclosed in Japanese Patent No. 2789560. Further, as a digital multifunction machine, “Image processing device” concerning image processing of a scanned signal, storage of images in memory, and concurrent operation of a plurality of functions has been disclosed in JP, H08-274986A, for example.
Conventionally, however, there has not been proposed any device, in a document scanning mechanism using the sheet-through type auto document feeder, which can automatically duplicate documents of various sizes while enlarging or reducing each of them. This is because, scaling size can not be determined in the conventional document scanning mechanism since document size can not be determined before starting the scanning of the document.
A method for realizing a device which can automatically duplicate documents of various sizes while enlarging or reducing each of them in the document scanning mechanism using the sheet-through type auto document feeder are known. However, this method requires to perform concurrent operation in processing units by making use of image memory. In this case, system configuration becomes complicated such as increase of the number of ports for transmitting image data or the like in order to effectively perform concurrent operation.